This contribution presents an experimental investigation and a numerical model of fatigue damage development in hardened cement paste at the micro-meter length scale. For the very first time, an experimental approach for measuring flexural fatigue of hardened cement paste specimens…
This contribution presents an experimental investigation and a numerical model of fatigue damage development in hardened cement paste at the micro-meter length scale. For the very first time, an experimental approach for measuring flexural fatigue of hardened cement paste specimens at the microscale has been developed. Microscopic cantilever specimens have been prepared and subjected to fatigue loading using a nanoindenter, with the aim of determining their fatigue life under different flexural stress levels (the so-called S-N curves). Compared to static fracture, microscopic images reveal an increased density of nano-scale cracks under fatigue loading. Based on the experimental data, a numerical model using a 2D lattice network approach for simulating the development of fatigue damage in hydrated cement paste at the microscale has been developed. The model uses segmented X-Ray computed tomography images as microstructural input. By assigning different mechanical and fatigue properties to different phases in the hydrated cement paste, it is possible to simulate the damage evolution in hardened cement pastes. A cyclic constitutive law is proposed for considering the fatigue damage evolution. The model is calibrated and validated using the experimental data from the tests described above and is shown to be able to reproduce well the flexural fatigue experiments in terms of S-N curves, stiffness degradation, and residual deformation. The proposed model can further be used as a basis for multi-scale analysis of fatigue in concrete.